General Principles and Evaluation of Tissue Flashcards
What is positive predictive value?
Given a positive test result, the probability that the individual has the condition
What is negative predictive value?
Given a negative test result, the probability that the individual does not have the condition
What is sensitivity?
Given that the individual has the condition, the probability that the test will be positive
What is specificity?
Given that the individual does not have the condition, the probability that the test will be negative
What is positive likelihood ratio?
Given a positive test, the increase in odds favoring the condition
What is negative likelihood ratio?
Given a negative test, the decrease in odds favoring the condition
5 Sources of error in imaging studies (same as any other diagnostic tests)
- Images from one patient may be mistaken for those of another patient
- Wrong extremity imaged
- Obvious injuries are imaged while other injuries missed
- Areas of referred pain rather than source of symptoms may be imaged
- Images may be misinterpreted by radiologist or referring provider
- Poor quality images
How do DPTs order images?
PTs may recommend type of imaging and appropriate sequences or views, but they must first understand the most current diagnostic standards
**US Army DPTs (direct access) hold
privileges for ordering imaging studies
What must the PT give the radiologist when requesting images?
- Description of mechanism of injury (MOI)
- Location of suspected pathology or areas of symptoms
*They appreciate brief but anatomically correct descriptions
What 2 things must you consider when interpreting images?
1) Comprehensive History
2) Physical Examination
What do radiologists often suggest on their official reports?
Clinical correlation of imaged pathology
Who’s job is it to interpret diagnostic images?
The radiologist
Info from the pt examination combined with this interpretation of images may reveal overlooked pathology on the official reading (PT responsibility)
3 Categories of Imaging
1) Reflective Imaging
2) Ionizing Radiation Imaging
3) Emission Imaging
2 Examples of reflective imaging
1) Ultrasound
2) Magnetic Resonance Imaging (MRI)
How does reflective imaging work?
Energy is inserted into the system, captured, and converted into an image when it is returned
3 Examples of ionizing radiation imaging
1) Standard X-Rays
2) Digital X-Rays
3) Computed Tomography (CT)
How does ionizing radiation imaging work?
Patient is exposed to ionizing radiation (associated risk) that penetrates matter and creates collectable image through the power of a computer
Ionizing Radiation is capable to produce an image or “slice” as narrow as __ mm thick
3
The computer software converts the x-rays that penetrate the body into ____ units.
Hounsfield
Hounsfield units represent how many levels of specificity between black and white?
over 2000 levels
Water = \_\_\_ units Air = \_\_\_ units Metal = \_\_\_ units
0
-1000
1000
What is the imaging of choice for evaluating bony pathology?
CT
What is the imaging of choice for evaluating soft tissue pathology?
MRI
Example of Emission imaging
Bone scan
How does emission imaging work?
Blood drawn and tagged with radiopharmaceutical agent, reintroduced to body, and allowed to circulate throughout entire body. As the radiopharmaceutical agent decays, it emits γ-rays. After about 2 or 3 hours the body is scanned with a scintillation camera to collect γ emissions which produce an image that demonstrates areas of increased metabolic activity (increased circulation)
What does a bone scan tell you?
It will tell you if an area demonstrates increased metabolic activity (cancer) but not what is causing increased metabolic activity
Bone scans are non-____ and not _____.
Specific
Diagnostic
When are bone scans used?
When trying to identify occult (nonrecognizable) injuries to skeletal system, demonstrating degenerative changes and for documenting extent of certain metastatic lesions
What are the most expensive types of imaging?
CT and MRI are the most expensive, followed by bone scans, and than standard films
What is the most common form of imaging?
Standard X-Rays (aka plain or routine film)
How do these conventional radiographs work?
They use ionizing radiation to produce high-resolution analogue images on specialized film
What are the 4 major densities of x-ray production?
from least to most dense
1) Air
2) Fat
3) Fluid
4) Bone
Air is the most radiolucent, what does that mean?
It absorbs the least number of particles from the beam which results in the darkest areas of the negative/film/plate
Where is air normally found on the film?
within the trachea, lugs, and colon
Fat is the also radiolucent, but absorbs ___ of the beam than air
MORE
Where is fat found on the film?
Varies between individuals, but can be found from subcutaneous tissue to pericardium and omentum surrounding the intestines
What does fluid represent on a film?
varying densities of soft tissue organs and muscle
What substance is the most dense?
Bone (represents white on the film)
Bone itself also varies in density. Cortical (outer) bone is ___ dense than cancellous (inner) bone
Much More
Bone is not called radiolucent rather it is considered radio-_____.
Opaque
Metals are completely radio-____.
opaque (therefore the least radiolucent) and appear white on a film
Typically what are radiographs used for?
- to demonstrate bone origin pathology
- relationship of bone structures
- relationship of foreign objects to skeletal structures
Are plain film radiographs sensitive to subtle pathology? What does this mean in reference to test results?
No, a significant change to the structure of bone must occur before radiographs reveals it.
This means that the chance of a false negative is high for subtle, early-stage pahtologies
What percent change in bone density is required in order for an x-ray to detect it?
30-40%
In order to reduce the radiation exposure and resultant cancer risk to breasts and the thyroid gland what view should be selected?
Posterior-to-anterior
How many exposures are required?
Minimum of two exposures taken at 90° to one another
How many exposures are required to cervical and lumbar spine?
five exposures each
